<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>换肤效果</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        body{
            background: url(images/1.jpg) no-repeat center top;
        }
        li{
            list-style: none;
        }
        .baidu{
            overflow: hidden;
            margin: 100px auto;
            background-color: #fff;
            width: 410px;
            padding-top: 3px;

        }
        .baidu li{
            float:left;
            margin:0 1px;
            cursor: pointer;
        }
        .baidu img{
            width: 100px;
        }
    </style>

</head>
<body>
    <ul class="baidu">
        <li><img src="images/1.jpg" alt=""></li>
        <li><img src="images/2.jpg" alt=""></li>
        <li><img src="images/3.jpg" alt=""></li>
        <li><img src="images/4.jpg" alt=""></li>
    </ul>
    <script>
        var imgs=document.querySelector('.baidu').querySelectorAll('img');
        for(var i=0;i<imgs.length;i++){
            imgs[i].onclick=function(){
                document.body.style.backgroundImage='url(' + this.src + ')';
            }
        }
    </script>
</body>
</html>